1. Field of the Invention
This invention relates to centrifugal casting of pipes. Although the method and apparatus of this invention will hereinafter be described primarily with reference to the manufacture of centrifugally cast glass filament reinforced pipes the invention is also applicable to other types of centrifugally cast pipes and other centrifugally cast articles.
2. Description of the Prior Art
In the known centrifugal casting process for glass reinforced plastic pipes, liquid resin and hardening agent are placed inside a rotating cylindrical mould along wit the required reinforcements and fillers in the appropriate order and amounts. The centrifugal force created by the rotation causes the solid materials to migrate through the liquid resin to the outer wall and compact in the normal way. The glass filaments usually take several minutes to compact fully due to the high viscosity of the liquid resin and the large specific surface area of the glass filaments. After an appropriate delay, heat is applied to the pipe either by blowing heated air along the bore of the uncured pipe or by applying heat to the outside of the mould through an appropriate medium such as heated air, oil or water. The heating accelerates the triggering of the curing of the resin and hardener. In either case, the heat is conducted through the surface of the pipe and must spread through the rest of the pipe wall by conduction. This is a slow process as most plastics are poor thermal conductors. These processes also often result in uneven heating of the pipe resulting in some parts of the pipe curing more slowly than other.